Fluororubbers are excellent in heat resistance, oil resistance, solvent resistance, chemical resistance, and other properties, and used as rubbers having excellent gasohol resistance and sour gasoline resistance. In recent years, these properties are becoming more important along with the strengthening of environmental regulations (e.g., gasoline volatility regulation), and fluororubbers are progressing at a higher degree of fluorination.
While fluororubbers have such excellent properties, they are more expensive than other rubber materials, such as NBR. Therefore, a rubber laminate in which an NBR layer is laminated on a fluororubber layer is used. However, there are problems that fluororubbers and NBR cannot be vulcanization-bonded by an ordinary method, or even if they are bonded to each other, the bonding strength therebetween is very weak.
Patent Document 1 discloses a laminate in which a fluorine-containing polymer layer and a diene-based polymer layer are firmly bonded to each other by heating, the fluorine-containing polymer layer containing:                (A) a 2-substituted-4,6-dithiol-s-triazine derivative;        (B) an oxide, hydroxide, or carbonate of an alkaline earth metal; and        (C) 1,8-diazabicyclo[5.4.0]undecene or a 2-ethylhexyl salt thereof, etc. and/or a quaternary ammonium salt, etc.Thus, the composition of the fluorine-containing polymer layer is devised on compounding; however, a fluororubber layer is used as the fluorine-containing polymer layer, causing problems that when the fluorine content in the fluororubber layer increases, sufficient bonding strength cannot be achieved, or peeling occurs at the bonding interface.        
Further, it is proposed that a quaternary onium salt is added to a fluororubber layer to be laminated on an NBR layer in the production of the fluororubber layer, as listed below.
(1) A double-layer rubber hose suitable as an automotive fuel hose, in which the fluororubber layer is composed of a ternary-based fluororubber that is a polyol based-vulcanization system together with a quaternary ammonium salt, and satisfies a specific vulcanization induction time (T10); and an NBR layer is composed of peroxide vulcanization system NBR, to which an active hydrogen-containing functional group is introduced (see Patent Document 2).
(2) A rubber laminate comprising a peroxide crosslinkable NBR composition containing a specific phosphonium salt, and a metal oxide-containing fluororubber composition (see Patent Document 3).
(3) A rubber laminate prepared by vulcanization-bonding of an unvulcanized fluororubber composition and an unvulcanized NBR composition containing sulfur (donating compound), an organic peroxide, and an organic phosphonium salt (see Patent Document 4).
(4) A fuel hose having an inner layer composed of fluororubber, and an outer layer composed of an NBR-PVC-blended polymer, wherein the PVC content in the blend material and the combined acrylonitrile content in NBR are controlled at a constant level, and a 1,8-diazabicyclo[5.4.0]undecene-7 salt of a carboxylic acid is added (see Patent Document 5).